We analyzed the diversity of nitrogenfixable bacterium communities in the rhizosphere of larch in different periods in Arxan region by traditional bacterial isolation and culture combined with 16S rDNA sequence analysis, so as to reveal the diversity of nitrogenfixable bacteria in the rhizosphere of larch and the seasonal variation rules of the community structure, and to provide theoretical basis for the sustainable development of forest ecosystem. The results show the following: (1) From Arxan Larix gmelinii rhizosphere soil, a total of 112 bacterium strains, isolation and purification of points belonging to 14 genera of 41 species. They include Pseudomonas, Burkholderia, Rhizobium, Phyllobacterium, Arthrobacter, Paenibacillus, Serratia, Erwinia, Curtobacterium, Bacillus, Enterobacter, Acinetbacter, Caulobacter, and Rhodococcus. Pseudomonas dominated among the bacterial isolates, followed by Phyllobacterium, Burkholderia and Arthrobacter. (2) Seasonal changes had a significant effect on the change of nitrogenfixing flora of larch, which showed that the most dominant group in April and October was Pseudomonas from the γproteobacteria. The most dominant groups in June and August were the same,but the composition was different. Both of them were gamma proteobacteria and actinomycetes. In June, the dominant bacterium groups included Pseudomonas, Curtobacterium, Rhodococcus and Arthrobacter. In August, the dominant bacterium groups were Pseudomonas, Acinetbacter, Enterobacter, Curtobacterium, Rhodococcus and Arthrobacter. (3) Species evenness index (McIntosh index) varies significantly in different periods, with the largest in August and the smallest in April, and the variation range is between 0.83 and 1.164. The ShannonWiener index was significantly higher in June and August than in April and October. Dominance index, Simpson index in April and October is significantly higher than in June and August. The results showed that the rhizosphere microbial diversity of larch in Arxan area was relatively high, and the communities were relatively complex. Most of the 14 isolated genera were rhizotrophic bacteria, and the community composition of nitrogenfixing bacteria in different periods was significantly affected by seasons.